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This article reviews therapeutic drug monitoring (TDM) use for current inflammatory bowel disease (IBD) treatments. IBD comprises Crohn’s disease and ulcerative colitis-chronic gastrointestinal inflammatory disorders. Treatment options for moderate to severe IBD include thiopurines; methotrexate; biologic agents targeting tumor necrosis factor, α4β7 integrin or interleukins 12 and 23; and Janus kinase inhibitors. TDM is recommended to guide treatment decisions for some of these agents. Published literature concerning TDM for IBD treatments was reviewed. S.D.L., R.S., and E.V.L. drew on their clinical experiences. Polymorphisms resulting in altered enzymatic activity inactivating thiopurine metabolites can lead to myelotoxicity and hepatotoxicity. Increased elimination of biologic agents can result from immunogenicity or higher disease activity, leading to low drug concentration and consequent nonresponse or loss of response. TDM may aid treatment and dose decisions for individual patients, based on monitoring metabolite levels for thiopurines, or serum drug trough concentration and antidrug antibody levels for biologic agents. Challenges remain around TDM implementation in IBD, including the lack of uniform assay methods and guidance for interpreting results. The Janus kinase inhibitor tofacitinib is not impacted by enzyme polymorphisms or disease activity, and is not expected to stimulate the formation of neutralizing antidrug antibodies. TDM is associated with implementation challenges, despite the recommendation of its use for guiding many IBD treatments. Newer small molecules with less susceptibility to patient variability factors may fulfill the unmet need of treatment options that do not require TDM, although further study is required to confirm this.

INTRODUCTION: Tofacitinib is an oral, small molecule JAK inhibitor for the treatment of ulcerative colitis (UC). Tofacitinib safety and efficacy were demonstrated in patients (pts) with moderate to severe UC in 3 Phase 3 studies, 1 and are being evaluated in an ongoing, open-label, long-term extension (OLE) study. 2 METHODS: We present updated safety and efficacy data from the OCTAVE Open OLE study (NCT01470612; Sep 2018; database not locked) 2 in completers/treatment failures in OCTAVE Sustain (NCT01458574) or non-responders in OCTAVE Induction 1/2 (NCT01465763/NCT01458951). Week (Wk) 8 data (OCTAVE Induction 1/2) and Wk 52 (completers) or early-termination data (OCTAVE Sustain) determined eligibility. Pts in remission (total Mayo score ≤2, no individual subscore >1, rectal bleeding subscore 0) at Wk 52 of OCTAVE Sustain (central read) received tofacitinib 5 mg twice daily (BID) in the OLE study; all others received 10 mg BID. At Month 2, all pts had endoscopy, and induction non-responders with no clinical response were withdrawn. Incidence rates (IRs; unique pts with events per 100 pt-years [PY]) for adverse events (AEs) of special interest were calculated. Efficacy endpoints were derived from Mayo score (local read). RESULTS: Of 944 pts receiving ≥1 tofacitinib dose (for up to 5.5 years), 175 (18.5%) and 769 (81.5%) received 5 and 10 mg BID, respectively (454 and 1550 PY, respectively). 337 (35.7%) pts discontinued due to insufficient clinical response and 78 (8.3%) due to AEs excl. worsening UC. The most frequent AE class was infections and infestations (52.1%). The most frequent AEs were nasopharyngitis (20.3%) and worsening UC (19.5%). IRs (95% CI) for “Tofacitinib All” were: serious infections 1.61 (1.10, 2.27); herpes zoster (all) 3.35 (2.58, 4.27); major adverse cardiovascular events 0.15 (0.03, 0.44); malignancies excl. non-melanoma skin cancer (NMSC) 0.85 (0.50, 1.36); and NMSC 0.81 (0.46, 1.32), with no clustering of malignancy type. Table 1 shows AEs and IRs by dose. No new safety risks were identified. Table 2 shows efficacy data at Month 36. CONCLUSION: In pts with UC in the OLE study, no new safety risks emerged at 5.5 years vs earlier OLE analyses 2 or with tofacitinib in rheumatoid arthritis. Efficacy data continue to support long-term efficacy of tofacitinib 5 or 10 mg BID up to 36 months beyond OCTAVE Sustain.